The present invention relates to a overedge sewing machine which is capable of executing not only overedge sewing but also flat stitch and double-chain stitch while switching them over to each other.
Conventionally, there has been developed a overedge sewing machine which is capable of flat stitch sewing and double-chain stitch sewing. Generally, to execute the flat stitch sewing, a needle plate must have a specific shape and also there is necessary a double-chain looper which operates separately from upper and lower loopers used to execute overedge sewing. And, a position, where a needle used to carry out the flat sewing operation and double-chain stitch sewing operation is moved vertically, is set such that it is shifted respectively right and left as well as back and forth in a cloth feeding direction with respect to the overedge sewing operation. For this reason, when carrying out the flat stitch sewing operation and double-stitch sewing operation, it is necessary to change the needle to a position different from a position which is used in the overedge sewing operation.
However, use of the structure requiring the abovementioned needle position change results in not only the complicated and large-sized sewing machine but also the poor efficiency of the operation thereof. In view of this, in order to improve them, as in a sewing machine which is disclosed in Japanese Patent Publication No. 07-112517 (U.S. Pat. No. 4,690,080) there is developed a sewing machine which can use a lower looper and a double-chain looper in combination by switching a drive mechanism, thereby being able to omit the above-mentioned change of the needle position.
However, even in such sewing-machine, a needle plate must be replaced between the overedge sewing operation and the flat stitch and double-chain stitch sewing operations. That is, due to the fact that, especially in executing the flat stitch sewing operation, the needle setting portion of the needle plate must have a specific shape, the needle plate must be replaced with an exclusively designed needle plate.